Case Studies of the Low-latitude F-region Field-aligned Irregularities Generation or Suppression During Geomagnetic Disturbances

Abstract:

The suppression or generation of the equatorial/low-latitude F-region field-aligned irregularities (FAIs) during geomagnetic disturbances largely depends on the competitive effects of storm-time perturbation electric fields. In this paper, we present case studies of the low-latitude F-region FAIs development during geomagnetic disturbance conditions using the observations from a very high frequency(VHF) coherent scatter radar installed at Fuke, Hainan Island of China (19.5ºN,109.1ºE; magnetic latitude 9.58ºN) and a collocated digisonde. In Case 1, VHF radar observations showed that FAIs occurred during post-sunset hours on consecutive days of 11-16 March 2015 but were absent in 17 March during 2015 St. Patrick’s Day storm. Analysis result suggests that the suppression of the FAIs development in dusk side over Hainan longitude during the storm was caused by the weakening of zonal electric field due to westward ionospheric disturbance dynamo electric field. In Cases 2 and 3, VHF radar observations showed freshly-generated FAIs plume initiated during post-midnight hours (after 03 LT) in low FAIs occurrence rate seasons. Further analysis shows that these post-midnight echoes were related to the abnormal uplift of post-midnight F layer. The rapid uplifts of F layer and the subsequent FAIs development in post-midnight sector over Hainan were believed to result from eastward perturbation of zonal electric field in night side which may due to the rapid northward turning of interplanetary magnetic field and/or substorm onset.